Means for and method of detecting the presence of carbon monoxide



Dec. 20, 1932. LJUNGGR-EN, 1,891,429

m nus FOR AND-METHOD 0F DETECTING THE PRESENCE OF CARBON MONOXIDE Filed Jan. 5, 1951' 1&1.

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Patented Dec. 20, 1932 UNITED STATES PATENT. OFFICE I GUSTAF mane-earn, or mini swnnnu MEANS FOR AND METHOD OF DETECTING THE PRESENCE OF CARBON MON OXIDE Application filed January 5, 1931, Serial No. 506,823, and in. Great Britain January 20, 1930.

The present invention relates to a method of and means for detecting the presence of carbon monoxide in dangerous proportions in the air, in a simple and reliable manner.

Most of the poisoning cases on record are actually caused by carbon monoxide in the air. rence in everyday life. This gas forms a normal ingredient of the exhaust gases from m ternal combustion engines and also of illuminating gases, such as coal gas and the like. It is a product obtained in all incomplete combustion processes in fire places or the like. Persons now living under industrialized conditions are thus often liable to encounter carbon monoxide and, unfortunately, industrial development tends to increase this danger still more. In many countries great attention has been paid to this question and many researches have been published on carbon monoxide and its occurrence. The attention of the public has, however, not been drawn to the fact that, carbon monoxide is to be considered as a very common cause of imperfect health in the form of fatigue, reduced capacity for work, dizziness, etc., which are the typical symptoms of a slight carbon monoxide poisoning. The most dangerous property of carbon monoxide lies in the fact that its presence is not noticed because it is completely devoid of smell, taste and colour. I It is not generally known to the public that the exhaust gases from an automobile engine conicle, i. e. nearly the same percentage as ordinary coal gas and that the proportion of carbon monoxide is particularly high whenthe that practically all employees suffered from This is due mainly to its common occur tain from five to nine per cent carbon monox taining the presence'of carbon monoxide in a simple and reliable manner.

Said means should preferably also render possible a quick estimation of the extent of the danger due to presence of the gas.

V The methods hitherto'known'for carbon monoxide in the air and for measuring the proportion thereof are too insensitive and slow and too complicated to attain any gen eral measure .of use amongst the public. There is a plurality. of different chemical methods based upon the reducing property of carbon monoxide. One of the oldest methods comprises the use of palladious chloride (Pdclg) said chloride being reduced by car bon monoxide which results in a dark colouring. This method may be applied in different ways. Either a paper is soaked, in the time of the examination, with a solution of palladious chloride and the blackening or browning observed, or the paper is beforehand prepared with palladious chloride and thoroughly moistened at the moment of the examination, the blackening or browning being then observed in the same manner as before. However, both of these methods are, in common with other methodsfor the same purpose, not very suitable in practice and give unsatisfactory results. As regards theformer method the values obtained in the examination if the solution is only a few days old are entirely different from those obtained when using a freshly prepared solution. The same can be said also about the second method using test paper prepared beforehand. Furthermore, the reaction takes place in both methods too slowly to give any really useful results. Even if the concentration of monoxide is dangerous to life it may in certain cases require up to ten minutes before the reaction clearly appears. At a less concentration, which however still may be veryunhealthy,

the papers often need to be exposed for 12 or even 24 hours before any reaction appears.

The present invention has for its object to provide a method more sensitive and more reliable than those hitherto known and to standardize the reaction means used in connection with the method so as to assure entirely uniform results under all circumstances. By the invention it is simultaneously renderec possible not only to ascertain quickly and safely the presence of carbon monoxide in quantities injurious to health but also to make an estimation of the proportion of monoxide present in the air.

The invention is based upon the following facts observed in connection with the known palladious chloride methods. In the reaction, hydrochloric acid is set free which may influence the reaction proper and also the coagulation of palladium. It is found that the reaction does not take place at the presence of dilute hydrochloric acid (for example 0.1 normal solution of H01) and that the acidity,

i. e. the hydrogen ion concentration, has a strong influence upon the reaction, as can be seen from the diagram in Fig. 1 on the accompanying drawing where the abscissa represents the hydrogen ion concentration, expressed in pH,a nd the ordinate represents the time 25 of reaction in minutes. As is clearly understood from the diagram'the reaction time is considerably increased if the hydrogen ion concentration becomes greater than 0.003 of normal solution pH less than 2.5) and that the rapidity of reaction quickly increases if the hydrogen ion concentration is reduced below said value. It is, however, not suitable to proceed beyond the neutral point, as hydrolysis of the palladious chloride than may occur which disturbs the reaction. There is thus a limited range for the values of the hydrogen ion concentration when the reaction proceeds at its optimum. The problem to limit the hydrogen ion concentration to said optimum is solved according to the invention by a further addition to the palladious salt of a re-agent namely a so called buffer substance i. e. av substance able to con- 'trol the hydrogen ion concentration and to maintain it at a fixed value. Such substances are used, by way of example, in enzyme chemistry.

In its simplest form the new method may be applied by moistening an ordinary palladious chloride paper with a solution of such a b'ufier substance. Such a procedure is, however, not practical, The method 'must be so simplified that the reaction may be carried out withoutsolutions of chemicals being available, besides which it is desirable, as above mentioned, to standardize a new reaction'means in order toincrease the uniformity of the reaction and to render possible a comparatively exact estimation of the percentage of carbon monoxide present, as

given by the reaction time. For this purpose the paper is prepared beforehand both with the palladious salt and with the buffer substance the ratio of concentration between the two substances being so selected that the concentration of the buffer substance expressed in equivalents is greater than the concentration of palladious chloride expressed in the same manner, the buffer substance being thus capableof suppressing the concentration of the hydro-chloric acid set free. To confine the values of the hydrogen ion concentration to a range permitting the reaction to proceed at its optimum, the buffer substance controlling the hydrogen ion concentration must be constituted by a salt of a strong base (for example, of an alkaline metal) and a weak acid the dissociationcoelficient of the latter being then preferably less than 0.001, In

the moistening of the paper ordinary water may then be used. As an example of a suitable buifer substance sodium acetate may be mentioned.

The researches carried out in connection characterize the paper not only in its unimpregnated statebut also after it has been impregnated by inorganic salts.

v 2. At higher concentrations of palladious chloride the test paper reacts more rapidly than at weaker concentrations. On the other hand, the paper is less durable the higher the concentration is. It has, however, been found that the concentration preferably should be kept between 0.1 and 0.5 percent. The most advantageous concentration has been found to be about 0.3 percent.

3. lVhen such a palladious chloride paper has been moistened with water the reaction takes place more or less rapidly according to the proportion of humidity. This is shown by the diagram in Fig. 2 where the abscissa represents the moisture m percent whereas the ordinate represents the reciprocal value of the reaction time. This pronounced in fluence of'the. moisture upon the reaction time makesit absolutely necessary to define the moisture in the reaction in order to render possible a standardization of the means employed. Said difliculty may, however, be avoided in a very simple manner by moistening the test paper only partially in such a manner that a transition zone with a defined ,moisture is obtained between the dry and.

the damp portion'of the paper. The moistenshould at the same time have good absorptive I properties which latter properties should ing is then carried out in the simplest manner by only putting a drop of water on the paper. Then the further advantage is gained that the concentration of palladious chloride is increased in the border zone proper on account of absorption. At the same time a durable paper is obtained by limiting the concentration of palladious chloride in preparing the paper. The increased rapidity of reaction resulting from a higher concentration is thus utilized by said method for applying the moisture.

a. The preferred manner of preparing the test paper according to the invention is to soak the same with a solution contalning both palladious chloride and a buffer substance of the kind referred to. The drying of the paper thus impregnated should be accelerated by using artificial means because, in using a slow drying process, the paper becomes browned which renders the observation of the reaction more difiicult. Besides, said artificial drying may be carried on further than the natural drying. It is to be observed that the drying should be applied uniformly to both sides of the paper.

At high carbon monoxide concentrations involving danger to life the paper according to the invention reacts instantly. The time required for the reaction of said papers at acarbon monoxide concentration of 0.2 per cent (which dose may result in the loss of life after inhalation for at least one hour) is twenty to twenty-five seconds and, in case of a concentration of 0.01 percent (considered as the weakest concentration which injuriously afiects the health after a prolonged inhalation, by way of example during a working day) a clearly distinguishable reaction is obtained after ten minutes. Said values refer to temperatures about 18 C. At temperatures about 0 C. the times are twice as long.

The test is so simple to carry out and the indication so distinct that the method can usefully be used by any person. The invention is not intended to represent an exact quantitative method, even if so used by a trained chemist, but it is intended to render possible a comparatively exact estimation of the order or degree of the carbon monoxide concentration so as to enable even a layman to ascertain the extent of actual danger of poisoning thereby.

I claim 1. A method for the production of reaction means for detecting carbon monoxide in quantities injurious to health in the air char acterized in that porous paper is impregnated with a palladious salt and also, in a higher concentration, with a salt of a strong base (such as of an alkaline metal) and a weak acid.

2. A method as claimed in claim 1, characterized by the dissociation coefficient. of the weak acid being less than 0.0001.

3. A method as claimed in claim 1, characterized in that the paper is soaked by means of a solution containing both the palladious salt and a bufier substance the latter having a higher concentration than the former.

4. A method as claimed in claim 1, characterized in that the paper is subjected to a rapid drying process by artificial means, the drying being carried out in such a manner that the drying rapidity is equal on both sides of the paper.

5. Reaction means for the detection of carbon monoxide in the air, comprising paper impregnated With a palladious salt and also a salt of a strong base and a weak acid, the latter salt having a higher concentration than the former.

6. A method for the production of reaction means for detecting carbon monoxide in quantities injurious to health in the air, in which a porous paper is soaked by means of a solution containing a palladious salt and also, in a higher concentration, a salt of a strong has; of an alkaline metal type and a weak aci In testimony whereof I afiix my signature.

GUSTAF LJUNGGREN.

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